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Overweight children: Are they at increased risk for severe injury in motor vehicle collisions?
Accident Analysis and Prevention 41 (2009) 959–962
Contents lists available at ScienceDirect
Accident Analysis and Prevention journal homepage: www.elsevier.com/locate/aap
Overweight children: Are they at increased risk for severe injury in motor vehicle collisions? Pavan P. Zaveri a,b,∗ , Danielle M. Morris c , Robert J. Freishtat a,b , Kathleen Brown a,b a b c
Division of Emergency Medicine, Children’s National Medical Center, United States School of Medicine and Health Sciences, George Washington University, United States Georgetown University School of Medicine, United States
a r t i c l e
i n f o
Article history: Received 9 June 2008 Received in revised form 20 April 2009 Accepted 23 May 2009 Keywords: Obesity, Pediatrics Motor vehicle collision Trauma
a b s t r a c t Background: Obesity is an epidemic in the United States. The relationship between traumatic injury and obesity in children is not well-studied. We hypothesized that overweight children suffer more severe injuries, different distributions of injuries and improper use of restraints in motor vehicle collisions. Methods: We conducted a secondary analysis of the CIREN database of motor vehicle collisions of subjects 2–17 years old. Overweight was defined as a BMI percentile for age >85%. Significant injury was an Injury Severity Score (ISS) >15 or an Abbreviated Injury Scale (AIS) score greater than one. Further analysis looked at injuries classified as head, trunk, or extremities and appropriateness of restraints. Odds ratios compared the overweight to lean groups. Results: 335 subjects met inclusion criteria with 35.5% of cases being overweight. For significant injury, overweight cases had an odds ratio of 1.2 [95% CI: 0.8–1.9]. Analysis by AIS for overall significant injury and to specific body regions also did not show any significant associations. Overweight versus lean subjects had an odds ratio of 1.3 [95% CI: 0.8–2.1] for improper use of restraints. Conclusions: We found no significant relationship between pediatric injury severity, distribution of injuries, or restraint use and being overweight. Limitations of this study were the small sample size in this database and the large number of unrestrained subjects. © 2009 Elsevier Ltd. All rights reserved.
1. Introduction Obesity has become an epidemic in the United States, particularly in the pediatric population (Krebs and Jacobson, 2003; O’Brien et al., 2004). The prevalence of overweight children has nearly doubled over the past several decades (MMWR, 2006). Many complications of obesity have been well-studied in the medical literature including diabetes, hypertension, renal disease, heart disease and others. A number of studies have been conducted in adults assessing the effects of obesity on outcomes from traumatic injuries (Choban et al., 1991; Boulanger et al., 1992; Bushard, 2002; Mock et al., 2002; Moran et al., 2002; Arbabi et al., 2003; Wang et al., 2003; Whitlock et al., 2003; Neville et al., 2004; Brown et al., 2005; Byrnes et al., 2005; Brown et al., 2006a; Zhu et al., 2006; Ryb and Dischinger, 2008).
∗ Corresponding author at: Children’s National Medical Center, Emergency Medicine and Trauma Center, 111 Michigan Ave., NW, Washington, DC 20010, United States. Tel.: +1 202 476 4872; fax: +1 202 476 3573. E-mail addresses: [email protected] (P.P. Zaveri), [email protected] (D.M. Morris), [email protected] (R.J. Freishtat), [email protected] (K. Brown). 0001-4575/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.aap.2009.05.011
For example, three studies demonstrated that severely overweight adults suffering trauma had significantly increased mortality rates (Choban et al., 1991; Neville et al., 2004; Ryb and Dischinger, 2008). Several smaller studies have looked specifically at injuries in obese patients resulting from motor vehicle collisions (Mock et al., 2002; Moran et al., 2002; Arbabi et al., 2003; Wang et al., 2003; Whitlock et al., 2003; Zhu et al., 2006). Many of these authors comment about the possible need to reconsider safety and design features of vehicles given these results. Even though traumatic injury is the number one cause of death in the pediatric population (Ludwig and Lavelle, 2000), its relationship with obesity has not been well-studied. One study of pediatric trauma patients found that overweight patients had longer hospital stays and more complications than lean counterparts (Brown et al., 2006a). To date, no study examining the relationship between obesity in children and injury severity in motor vehicle collisions has been published. We chose to look at this using an existing database that includes the weight, height and injury severity of children involved in motor vehicle collisions. This database also contains information on the forces exerted during the collision and what types of restraint were used by the cases. We formulated hypotheses given that obesity creates a disproportionate body habitus leading to undue or unex-
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P.P. Zaveri et al. / Accident Analysis and Prevention 41 (2009) 959–962
pected forces on the body and can also be a consideration for proper choice and use of child restraint systems. We hypothesized that overweight children suffer more severe injuries in motor vehicle collisions than their lean counterparts. We also hypothesized that the distribution of injuries by region of the body would be different in overweight versus lean children and that overweight children would be more likely to be incorrectly restrained in motor vehicle collisions.
of Automotive Medicine, 1990). ISS is calculated based on the sum of the squares of the highest AIS codes in the three most severely injured body regions (Baker et al., 1974; Baker and O’Neill, 1976). The AIS classifies the injuries into eight regions. For the injury pattern analysis, we have condensed the regions into three: head, trunk and extremity. For statistical analysis, ISS was dichotomized with ISS >15 equaling seriously injured. AIS was also divided with AIS ≥2 defined as significant injury and AIS <2 as minor injury.
2. Methods
2.3. Determination of appropriate restraint use
The Crash Injury Research and Engineering Network (CIREN) project was the source of data for this study. It is an ongoing project examining crash reconstruction, medical data and careful analysis of the biomechanical forces causing injury. Each case contains numerous data points regarding detailed characteristics about the patient, vehicle, crash scene, injuries and results. A multidisciplinary team involving emergency medical services, police, crash reconstructionists, biomechanical or mechanical engineers, physicians, and nurses gather and review the data entered into the database. The patient data to be used for this study has been collected at eight level 1 trauma centers as part of the CIREN project. Cases for the database are chosen as a convenience sample of patients who present to these centers after a motor vehicle collision, had injuries and are evaluated for their injuries and consented to be part of the database. Subjects for this study were all patients entered in the CIREN database age 2–17 years. Patients without both a height and weight recorded were excluded, as body mass index (BMI) could not be calculated for these patients.
We reviewed the type of restraint used for each patient with particular attention to its appropriateness, based on the current American Academy of Pediatrics (AAP) recommendations for child safety restraints. The AAP recommends that infants from birth to 12 months and less than 20 pounds should be in a rear-facing infant safety seat. Toddlers from 12 months and 20 pounds to 40 pounds should use a forward-facing child safety seat. Children greater than 40 pounds and less than 8 years old and 57 in. tall should use a belt-positioning booster seat. Finally, a child should be approximately 57 in. tall and at least 8 years old before moving to the three-point belt restraint standard in vehicles today (American Academy of Pediatrics, 2007). After determining the appropriateness of restraints for each patient, we compared the percentage of overweight children that were improperly restrained to that of lean children.
2.1. Determination of overweight We used patient age, gender, weight, and height to determine the body mass index percentile. Subjects with a BMI of greater than or equal to the 85th percentile for age were categorized as overweight; those less than the 85th percentile were considered lean. The overweight category included those children at risk of being overweight between the 85th and 95th percentile (Krebs and Jacobson, 2003; Himes and Dietz, 1994). The percentiles charts are based on population data gathered from various parts of the United States between 1963 and 1994 and are recommended as the standard to assess for overweight children (Ogden et al., 2002).
2.4. Statistical analysis Initial power analysis demonstrated a need for 150 cases in each group, overweight and lean, to achieve a power of 80% and detect an odds ratio as small as 1.8. Odds ratios were calculated comparing lean and overweight groups for overall injury and various subsets of injuries to identify relationships. Further simple linear regression was performed to confirm results. Data were analyzed with SPSS 12.0 (SPSS, Inc., Chicago, IL) using Mann–Whitney test for ordinal and non-normal continuous variables to determine statistical significance. This study received exemption status from our institutional review board as it was an analysis of a de-identified dataset. 3. Results 3.1. Subjects
2.2. Determination of injury severity In the process of the development of the CIREN database, each injury is evaluated by a multi-disciplinary team and graded as to its severity using the Injury Severity Score (ISS) and the Abbreviated Injury Scale (AIS). Each injury is assigned an AIS code between 1 (minor) and 6 (fatal) (Association for the Advancement
We found 405 cases between ages 2 and 17 years in the CIREN database of 2935 cases. Of these, 335 cases were identified with complete information meeting inclusion criteria. The median age was 10.1 years (IQR, 6–16). Overall, 48% were male. The two groups were similar in total velocity of impact (V) and seating row (Table 1). Significant differences were noted between the over-
Table 1 Subject characteristics.
Total number Median Age (years, IQR) Male gender, N (%) Median maximum intrusion (cm, IQR) Median total velocity (km/h, IQR) Seating row, N (%)
Median BMI (kg/m2 , IQR) Median BMI percentile for age (%, IQR)
First row Second row Third row
Overweight
Lean
p-Value
119 7.8 (5, 15) 69 (58) 18 (0, 32) 34 (27, 45)
216 11.4 (7, 16) 93 (43) 23 (9,39) 34 (25, 48)
0.001 0.012 0.019 0.978
116 (54) 88 (41) 12 (6)
0.423 0.580 Reference
68 (57) 47 (39) 4 (3) 21.3 (19, 26) 95 (91, 98)
17.5 (16, 21) 53 (22, 71)
<0.001 <0.001
P.P. Zaveri et al. / Accident Analysis and Prevention 41 (2009) 959–962
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Table 2 Injury severity and restraint use by overweight status.
Severe injury (ISS ≥ 15) Severe injury (ISS ≥ 15) (comparing overweight to lean) Fatality Any one severe injury (AIS ≥ 2) Any severe head injury (AIS ≥ 2) Any severe trunk injury (AIS ≥ 2) Any severe extremity injury (AIS ≥ 2) Inappropriately restrained a
Overweight N = 119 (%)
Lean N = 216 (%)
OR
58 (49) 31 (50)a 15 (13) 111 (93) 77 (65) 62 (52) 27 (23) 70 (59)
94 (44) 94 (44) 19 (9) 205 (95) 123 (57) 122 (56) 70 (32) 112 (52)
1.2 1.3 0.7 0.7 1.4 0.8 0.6 1.3
95% CI 0.8–1.9 0.7–2.3 0.3–1.4 0.3–1.9 0.9–2.2 0.5–1.3 0.4–1.0 0.8–2.1
p-Value 0.36 0.37 0.27 0.62 0.20 0.36 0.04 0.25
For overweight only, defined as BMI >95th percentile, N = 62. Cases at risk for overweight were excluded.
ratios for overweight versus lean children suffering significant head and significant trunk injuries were 1.4 (95% CI: 0.9–2.2) and 0.8 (95% CI: 0.5–1.3), respectively. Overweight cases had an odds ratio of 0.6 (95% CI: 0.4–1.0) versus lean cases of suffering a significant extremity injury. 3.4. Restraint pattern Fifty-four percent of cases who met inclusion criteria were improperly restrained based on current AAP recommendations. Overweight patients had 1.3 times the odds of being improperly restrained compared to lean cases, with a 95% confidence interval of 0.8–2.1. (Table 2).
Fig. 1. Distribution of BMI percentile for age.
weight and lean groups in age, gender and maximum intrusion (Table 1). After determining BMI percentile for age, overall 35.5% were overweight with the distribution displayed in Fig. 1. 3.2. Overall injury severity We examined ISS as the primary marker of overall severity. We determined that overweight children had 1.2 times the odds of suffering severe injuries than lean patients; however, with a 95% confidence interval of 0.8–1.9, this result is not statistically significant. Further delineating the risk by only looking at overweight patients (BMI percentile for age >95th), we compared those to cases with BMI below the 85th percentile for age. We found that overweight cases had 1.3 times the odds of suffering severe injury (ISS > 15). However, with a 95% confidence interval of 0.7–2.3, this also indicates a lack of association between overweight and injury severity. (Table 2). Given the negative result, we further performed simple linear regression analysis to detect a relationship. In linear regression, injury severity showed significant relationships with change in velocity (V), maximum intrusion and fatality. For age and overweight status, the p-values were not significant. (Table 3). 3.3. Injury pattern We looked at injury pattern by determining odds ratios for overweight and lean cases based on AIS codes. The odds ratio for overweight versus lean patients of having any significant (AIS 2+) injury was 0.7 with a 95% confidence interval of 0.3–1.9. The odds Table 3 Linear regression analysis for Injury Severity Score. Variable
Parameter estimate (ˇ)
95% CI
p-Value
Age Total delta V (kph) Maximum intrusion Overweight Fatality
0.320 0.145 0.111 0.962 33.098
−0.01–0.65 0.04–0.25 0.03–0.19 −4.17–2.24 27.76–38.44
0.057 0.008 0.007 0.555 0.000
4. Discussion Our analysis of this database did not show a significant association between overall injury severity in children injured in a motor vehicle collision and being overweight. A significant limitation of this study was the small number of cases identified. Therefore, it is possible we are missing a significant relationship because we did not have a sufficient number of cases. On the other hand, our study was powered to detect an odds ratio for overall severe injury in overweight versus lean cases of as low as 1.8. Furthermore, when looking at only overweight cases (>95th percentile for age), no statistically significant relationship could be identified. (Table 2) Furthermore, given that this database only had injured cases, we are not able to assess whether lean children are more likely to be not injured than overweight children. Other studies comparing the CIREN database to other collision databases such as the National Automotive Sampling System have found the population characteristics of the cases to be similar with a preponderance of more severely injured cases, as may have confounded our study (Ryb and Dischinger, 2008; Brown et al., 2006b). Analysis of the odds of suffering an injury to a particular body region in overweight versus lean cases did show decreased odds for overweight cases suffering a significant extremity injury. This suggests that being overweight protects against extremity injuries. However, since the statistical significance was relatively weak (the upper limit of the 95% CI is 1.0) the clinical significance of this finding is unclear and a larger case series may need to be analyzed to confirm this association. A troubling finding in this study was that over half the cases were inappropriately restrained according to AAP recommendations. National Highway Traffic Safety Administration data from a 2000 report of rates of unrestrained children in motor vehicles ranged from as low as 5–10% in a cross-sectional survey to as high as 56% in motor vehicle collisions with a fatality (National Highway Traffic Safety Administration, 2007). Since we were applying the 2006 AAP guidelines for child restraints on a period of time starting 10 years prior, that number may be artificially elevated. In addition, this database was a convenience sample of patients. This may bias towards those who were not properly restrained being included in
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the database. This finding may also have confounded our results by selecting for more severely injured patients that would decrease the variability in injury severity and make it more difficult to differentiate any kind of relationship between severity and overweight status. Regarding the subject characteristics, our sample showed a distribution of overweight cases to be 35% of the cases. Other recent studies show similar distributions of overweight in pediatric patients (MMWR, 2006; Ogden et al., 2008). The incongruence in that 35% of cases fall in the top 15th percentile is a reflection of the increasing prevalence of overweight children in the population. A deliberate choice was made in creating the percentile charts to not include data from the most recent prevalence studies which reflect increased obesity to avoid misclassification of overweight children (Ogden et al., 2002). This further underscores the importance of evaluating overweight children and their possible risk for injuries or disease. A further limitation in looking at the subject characteristics is the significant preponderance of males in the overweight group. However, as some studies of overweight children show that more males than females are overweight, this difference is not unexpected (MMWR, 2006). Another group characteristic showing significant differences was age with the lean group being older than the overweight group. The small number of total cases may have been the limiting factor in demonstrating this difference. Nonetheless, the lack of difference in outcomes makes this disparity unimportant. Finally, the maximum intrusion was significantly greater in the lean group. Once again with no difference in the outcomes, this characteristic is likely irrelevant. In spite of this negative study focusing on overall injury severity, Brown’s study of pediatric patients admitted to intensive care units (ICU) after trauma describes worse outcomes for overweight pediatric patients after traumatic injuries with more complications and longer ICU stays in the obese patients, though less severe head injuries and no difference in overall severity of injury. However, the cohort was limited to severely injured patients only (Brown et al., 2006a). Adult studies also show worse outcomes for obese motor vehicle collision occupants. In a small study, Whitlock et al., found that adults with a higher BMI may be twice as likely to have a driver injury (Whitlock et al., 2003). Three further studies demonstrated that a higher BMI was associated with increased mortality in a motor vehicle collision (Arbabi et al., 2003; Zhu et al., 2006; Ryb and Dischinger, 2008). Finally, Mock et al., showed that each kilogram increase in weight increased risk of mortality in adults (Mock et al., 2002). Further larger studies and population-based studies may delineate a difference not appreciated here. Alternatively, looking at other markers of outcomes may show a disparity of clinical and statistical significance. Obesity will continue to be an epidemic to fight with its higher morbidity and mortality compared to the lean population. Disclaimer Data was provided by the Crash Injury Research and Engineering Network (CIREN) Project at the United States Department of Transportation/National Highway Traffic Safety Administration
(USDOT/NHTSA). Views expressed are those of the authors and may not represent the views of NHTSA. References American Academy of Pediatrics (2007). Car Safety Seats: A Guide for Families 2007. Retrieved September 10, 2007, from www.webcitation.org/5RkeABg9s. Arbabi, S., Wahl, W.L., et al., 2003. The cushion effect. J. Trauma 54 (6), 1090–1093. Association for the Advancement of Automotive Medicine (1990). The Abbreviated Injury Scale, Des Plaines, IL, Association for the Advancement of Automotive Medicine. Baker, S.P., O’Neill, B., 1976. The injury severity score: an update. J. Trauma 16 (11), 882–885. Baker, S.P., O’Neill, B., et al., 1974. The injury severity score: a method for describing patients with multiple injuries and evaluating emergency care. J. Trauma 14 (3), 187–196. Boulanger, B.R., Milzman, D., et al., 1992. Body habitus as a predictor of injury pattern after blunt trauma. J. Trauma 33 (2), 228–232. Brown, C.V., Neville, A.L., et al., 2005. The impact of obesity on the outcomes of 1 153 critically injured blunt trauma patients. J. Trauma 59 (5), 1048–1051 (discussion 1051). Brown, C.V., Neville, A.L., et al., 2006a. The impact of obesity on severely injured children and adolescents. J. Pediatr. Surg. 41 (1), 88–91 (discussion 88–91). Brown, J.K., Jing, Y., et al., 2006b. Patterns of severe injury in pediatric car crash victims: Crash Injury Research Engineering Network database. J. Pediatr. Surg. 41 (2), 362–367. Bushard, S., 2002. Trauma in patients who are morbidly obese. AORN J. 76 (4), 585–589. Byrnes, M.C., McDaniel, M.D., et al., 2005. The effect of obesity on outcomes among injured patients. J. Trauma 58 (2), 232–237. Choban, P.S., Weireter Jr., L.J., et al., 1991. Obesity and increased mortality in blunt trauma. J. Trauma 31 (9), 1253–1257. Himes, J.H., Dietz, W.H., 1994. Guidelines for overweight in adolescent preventive services: recommendations from an expert committee The Expert Committee on Clinical Guidelines for Overweight in Adolescent Preventive Services. Am. J. Clin. Nutr. 59 (2), 307–316. Krebs, N.F., Jacobson, M.S., 2003. Prevention of pediatric overweight and obesity. Pediatrics 112 (2), 424–430. Ludwig, S., Lavelle, J., 2000. Resuscitation—pediatric basic and advanced life support. In: Fleisher, G., Ludwig, S., Henretig, F. (Eds.), Textbook of Pediatric Emergency Medicine. Williams and Wilkins, Baltimore, Lippincott, pp. 3–32. MMWR, 2006. Overweight among students in grades K-12—Arkansas, 2003-04 and 2004-05 school years. MMWR Morb. Mortal. Wkly. Rep. 55 (1), 5–8. Mock, C.N., Grossman, D.C., et al., 2002. The relationship between body weight and risk of death and serious injury in motor vehicle crashes. Accid. Anal. Prev. 34 (2), 221–228. Moran, S.G., McGwin Jr., G., et al., 2002. Injury rates among restrained drivers in motor vehicle collisions: the role of body habitus. J. Trauma 52 (6), 1116–1120. National Highway Traffic Safety Administration (2007). “Traffic Safety Facts 2000: Children.” Retrieved September 10, 2007, 2007, from www.webcitation. org/5RkdxUrNQ. Neville, A.L., Brown, C.V., et al., 2004. Obesity is an independent risk factor of mortality in severely injured blunt trauma patients. Arch. Surg. 139 (9), 983–987. O’Brien, S.H., Holubkov, R., et al., 2004. Identification, evaluation, and management of obesity in an academic primary care center. Pediatrics 114 (2), e154–e159. Ogden, C.L., Kuczmarski, R.J., et al., 2002. Centers for Disease Control and Prevention 2000 growth charts for the United States: improvements to the 1977 National Center for Health Statistics version. Pediatrics 109 (1), 45–60. Ogden, C.L., Carroll, M.D., et al., 2008. High body mass index for age among US children and adolescents 2003–2006. JAMA 299 (20), 2401–2405. Ryb, G.E., Dischinger, P.C., 2008. Injury severity and outcome of overweight and obese patients after vehicular trauma: a crash injury research and engineering network (CIREN) study. J. Trauma 64 (2), 406–411. Wang, S.C., Bednarski, B., et al., 2003. Increased depth of subcutaneous fat is protective against abdominal injuries in motor vehicle collisions. Annu. Proc. Assoc. Adv. Automot. Med. 47, 545–559. Whitlock, G., Norton, R., et al., 2003. Is body mass index a risk factor for motor vehicle driver injury? A cohort study with prospective and retrospective outcomes. Int. J. Epidemiol. 32 (1), 147–149. Zhu, S., Layde, P.M., et al., 2006. Obesity and risk for death due to motor vehicle crashes. Am. J. Public Health 96 (4), 734–739.
Contents lists available at ScienceDirect
Accident Analysis and Prevention journal homepage: www.elsevier.com/locate/aap
Overweight children: Are they at increased risk for severe injury in motor vehicle collisions? Pavan P. Zaveri a,b,∗ , Danielle M. Morris c , Robert J. Freishtat a,b , Kathleen Brown a,b a b c
Division of Emergency Medicine, Children’s National Medical Center, United States School of Medicine and Health Sciences, George Washington University, United States Georgetown University School of Medicine, United States
a r t i c l e
i n f o
Article history: Received 9 June 2008 Received in revised form 20 April 2009 Accepted 23 May 2009 Keywords: Obesity, Pediatrics Motor vehicle collision Trauma
a b s t r a c t Background: Obesity is an epidemic in the United States. The relationship between traumatic injury and obesity in children is not well-studied. We hypothesized that overweight children suffer more severe injuries, different distributions of injuries and improper use of restraints in motor vehicle collisions. Methods: We conducted a secondary analysis of the CIREN database of motor vehicle collisions of subjects 2–17 years old. Overweight was defined as a BMI percentile for age >85%. Significant injury was an Injury Severity Score (ISS) >15 or an Abbreviated Injury Scale (AIS) score greater than one. Further analysis looked at injuries classified as head, trunk, or extremities and appropriateness of restraints. Odds ratios compared the overweight to lean groups. Results: 335 subjects met inclusion criteria with 35.5% of cases being overweight. For significant injury, overweight cases had an odds ratio of 1.2 [95% CI: 0.8–1.9]. Analysis by AIS for overall significant injury and to specific body regions also did not show any significant associations. Overweight versus lean subjects had an odds ratio of 1.3 [95% CI: 0.8–2.1] for improper use of restraints. Conclusions: We found no significant relationship between pediatric injury severity, distribution of injuries, or restraint use and being overweight. Limitations of this study were the small sample size in this database and the large number of unrestrained subjects. © 2009 Elsevier Ltd. All rights reserved.
1. Introduction Obesity has become an epidemic in the United States, particularly in the pediatric population (Krebs and Jacobson, 2003; O’Brien et al., 2004). The prevalence of overweight children has nearly doubled over the past several decades (MMWR, 2006). Many complications of obesity have been well-studied in the medical literature including diabetes, hypertension, renal disease, heart disease and others. A number of studies have been conducted in adults assessing the effects of obesity on outcomes from traumatic injuries (Choban et al., 1991; Boulanger et al., 1992; Bushard, 2002; Mock et al., 2002; Moran et al., 2002; Arbabi et al., 2003; Wang et al., 2003; Whitlock et al., 2003; Neville et al., 2004; Brown et al., 2005; Byrnes et al., 2005; Brown et al., 2006a; Zhu et al., 2006; Ryb and Dischinger, 2008).
∗ Corresponding author at: Children’s National Medical Center, Emergency Medicine and Trauma Center, 111 Michigan Ave., NW, Washington, DC 20010, United States. Tel.: +1 202 476 4872; fax: +1 202 476 3573. E-mail addresses: [email protected] (P.P. Zaveri), [email protected] (D.M. Morris), [email protected] (R.J. Freishtat), [email protected] (K. Brown). 0001-4575/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.aap.2009.05.011
For example, three studies demonstrated that severely overweight adults suffering trauma had significantly increased mortality rates (Choban et al., 1991; Neville et al., 2004; Ryb and Dischinger, 2008). Several smaller studies have looked specifically at injuries in obese patients resulting from motor vehicle collisions (Mock et al., 2002; Moran et al., 2002; Arbabi et al., 2003; Wang et al., 2003; Whitlock et al., 2003; Zhu et al., 2006). Many of these authors comment about the possible need to reconsider safety and design features of vehicles given these results. Even though traumatic injury is the number one cause of death in the pediatric population (Ludwig and Lavelle, 2000), its relationship with obesity has not been well-studied. One study of pediatric trauma patients found that overweight patients had longer hospital stays and more complications than lean counterparts (Brown et al., 2006a). To date, no study examining the relationship between obesity in children and injury severity in motor vehicle collisions has been published. We chose to look at this using an existing database that includes the weight, height and injury severity of children involved in motor vehicle collisions. This database also contains information on the forces exerted during the collision and what types of restraint were used by the cases. We formulated hypotheses given that obesity creates a disproportionate body habitus leading to undue or unex-
960
P.P. Zaveri et al. / Accident Analysis and Prevention 41 (2009) 959–962
pected forces on the body and can also be a consideration for proper choice and use of child restraint systems. We hypothesized that overweight children suffer more severe injuries in motor vehicle collisions than their lean counterparts. We also hypothesized that the distribution of injuries by region of the body would be different in overweight versus lean children and that overweight children would be more likely to be incorrectly restrained in motor vehicle collisions.
of Automotive Medicine, 1990). ISS is calculated based on the sum of the squares of the highest AIS codes in the three most severely injured body regions (Baker et al., 1974; Baker and O’Neill, 1976). The AIS classifies the injuries into eight regions. For the injury pattern analysis, we have condensed the regions into three: head, trunk and extremity. For statistical analysis, ISS was dichotomized with ISS >15 equaling seriously injured. AIS was also divided with AIS ≥2 defined as significant injury and AIS <2 as minor injury.
2. Methods
2.3. Determination of appropriate restraint use
The Crash Injury Research and Engineering Network (CIREN) project was the source of data for this study. It is an ongoing project examining crash reconstruction, medical data and careful analysis of the biomechanical forces causing injury. Each case contains numerous data points regarding detailed characteristics about the patient, vehicle, crash scene, injuries and results. A multidisciplinary team involving emergency medical services, police, crash reconstructionists, biomechanical or mechanical engineers, physicians, and nurses gather and review the data entered into the database. The patient data to be used for this study has been collected at eight level 1 trauma centers as part of the CIREN project. Cases for the database are chosen as a convenience sample of patients who present to these centers after a motor vehicle collision, had injuries and are evaluated for their injuries and consented to be part of the database. Subjects for this study were all patients entered in the CIREN database age 2–17 years. Patients without both a height and weight recorded were excluded, as body mass index (BMI) could not be calculated for these patients.
We reviewed the type of restraint used for each patient with particular attention to its appropriateness, based on the current American Academy of Pediatrics (AAP) recommendations for child safety restraints. The AAP recommends that infants from birth to 12 months and less than 20 pounds should be in a rear-facing infant safety seat. Toddlers from 12 months and 20 pounds to 40 pounds should use a forward-facing child safety seat. Children greater than 40 pounds and less than 8 years old and 57 in. tall should use a belt-positioning booster seat. Finally, a child should be approximately 57 in. tall and at least 8 years old before moving to the three-point belt restraint standard in vehicles today (American Academy of Pediatrics, 2007). After determining the appropriateness of restraints for each patient, we compared the percentage of overweight children that were improperly restrained to that of lean children.
2.1. Determination of overweight We used patient age, gender, weight, and height to determine the body mass index percentile. Subjects with a BMI of greater than or equal to the 85th percentile for age were categorized as overweight; those less than the 85th percentile were considered lean. The overweight category included those children at risk of being overweight between the 85th and 95th percentile (Krebs and Jacobson, 2003; Himes and Dietz, 1994). The percentiles charts are based on population data gathered from various parts of the United States between 1963 and 1994 and are recommended as the standard to assess for overweight children (Ogden et al., 2002).
2.4. Statistical analysis Initial power analysis demonstrated a need for 150 cases in each group, overweight and lean, to achieve a power of 80% and detect an odds ratio as small as 1.8. Odds ratios were calculated comparing lean and overweight groups for overall injury and various subsets of injuries to identify relationships. Further simple linear regression was performed to confirm results. Data were analyzed with SPSS 12.0 (SPSS, Inc., Chicago, IL) using Mann–Whitney test for ordinal and non-normal continuous variables to determine statistical significance. This study received exemption status from our institutional review board as it was an analysis of a de-identified dataset. 3. Results 3.1. Subjects
2.2. Determination of injury severity In the process of the development of the CIREN database, each injury is evaluated by a multi-disciplinary team and graded as to its severity using the Injury Severity Score (ISS) and the Abbreviated Injury Scale (AIS). Each injury is assigned an AIS code between 1 (minor) and 6 (fatal) (Association for the Advancement
We found 405 cases between ages 2 and 17 years in the CIREN database of 2935 cases. Of these, 335 cases were identified with complete information meeting inclusion criteria. The median age was 10.1 years (IQR, 6–16). Overall, 48% were male. The two groups were similar in total velocity of impact (V) and seating row (Table 1). Significant differences were noted between the over-
Table 1 Subject characteristics.
Total number Median Age (years, IQR) Male gender, N (%) Median maximum intrusion (cm, IQR) Median total velocity (km/h, IQR) Seating row, N (%)
Median BMI (kg/m2 , IQR) Median BMI percentile for age (%, IQR)
First row Second row Third row
Overweight
Lean
p-Value
119 7.8 (5, 15) 69 (58) 18 (0, 32) 34 (27, 45)
216 11.4 (7, 16) 93 (43) 23 (9,39) 34 (25, 48)
0.001 0.012 0.019 0.978
116 (54) 88 (41) 12 (6)
0.423 0.580 Reference
68 (57) 47 (39) 4 (3) 21.3 (19, 26) 95 (91, 98)
17.5 (16, 21) 53 (22, 71)
<0.001 <0.001
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Table 2 Injury severity and restraint use by overweight status.
Severe injury (ISS ≥ 15) Severe injury (ISS ≥ 15) (comparing overweight to lean) Fatality Any one severe injury (AIS ≥ 2) Any severe head injury (AIS ≥ 2) Any severe trunk injury (AIS ≥ 2) Any severe extremity injury (AIS ≥ 2) Inappropriately restrained a
Overweight N = 119 (%)
Lean N = 216 (%)
OR
58 (49) 31 (50)a 15 (13) 111 (93) 77 (65) 62 (52) 27 (23) 70 (59)
94 (44) 94 (44) 19 (9) 205 (95) 123 (57) 122 (56) 70 (32) 112 (52)
1.2 1.3 0.7 0.7 1.4 0.8 0.6 1.3
95% CI 0.8–1.9 0.7–2.3 0.3–1.4 0.3–1.9 0.9–2.2 0.5–1.3 0.4–1.0 0.8–2.1
p-Value 0.36 0.37 0.27 0.62 0.20 0.36 0.04 0.25
For overweight only, defined as BMI >95th percentile, N = 62. Cases at risk for overweight were excluded.
ratios for overweight versus lean children suffering significant head and significant trunk injuries were 1.4 (95% CI: 0.9–2.2) and 0.8 (95% CI: 0.5–1.3), respectively. Overweight cases had an odds ratio of 0.6 (95% CI: 0.4–1.0) versus lean cases of suffering a significant extremity injury. 3.4. Restraint pattern Fifty-four percent of cases who met inclusion criteria were improperly restrained based on current AAP recommendations. Overweight patients had 1.3 times the odds of being improperly restrained compared to lean cases, with a 95% confidence interval of 0.8–2.1. (Table 2).
Fig. 1. Distribution of BMI percentile for age.
weight and lean groups in age, gender and maximum intrusion (Table 1). After determining BMI percentile for age, overall 35.5% were overweight with the distribution displayed in Fig. 1. 3.2. Overall injury severity We examined ISS as the primary marker of overall severity. We determined that overweight children had 1.2 times the odds of suffering severe injuries than lean patients; however, with a 95% confidence interval of 0.8–1.9, this result is not statistically significant. Further delineating the risk by only looking at overweight patients (BMI percentile for age >95th), we compared those to cases with BMI below the 85th percentile for age. We found that overweight cases had 1.3 times the odds of suffering severe injury (ISS > 15). However, with a 95% confidence interval of 0.7–2.3, this also indicates a lack of association between overweight and injury severity. (Table 2). Given the negative result, we further performed simple linear regression analysis to detect a relationship. In linear regression, injury severity showed significant relationships with change in velocity (V), maximum intrusion and fatality. For age and overweight status, the p-values were not significant. (Table 3). 3.3. Injury pattern We looked at injury pattern by determining odds ratios for overweight and lean cases based on AIS codes. The odds ratio for overweight versus lean patients of having any significant (AIS 2+) injury was 0.7 with a 95% confidence interval of 0.3–1.9. The odds Table 3 Linear regression analysis for Injury Severity Score. Variable
Parameter estimate (ˇ)
95% CI
p-Value
Age Total delta V (kph) Maximum intrusion Overweight Fatality
0.320 0.145 0.111 0.962 33.098
−0.01–0.65 0.04–0.25 0.03–0.19 −4.17–2.24 27.76–38.44
0.057 0.008 0.007 0.555 0.000
4. Discussion Our analysis of this database did not show a significant association between overall injury severity in children injured in a motor vehicle collision and being overweight. A significant limitation of this study was the small number of cases identified. Therefore, it is possible we are missing a significant relationship because we did not have a sufficient number of cases. On the other hand, our study was powered to detect an odds ratio for overall severe injury in overweight versus lean cases of as low as 1.8. Furthermore, when looking at only overweight cases (>95th percentile for age), no statistically significant relationship could be identified. (Table 2) Furthermore, given that this database only had injured cases, we are not able to assess whether lean children are more likely to be not injured than overweight children. Other studies comparing the CIREN database to other collision databases such as the National Automotive Sampling System have found the population characteristics of the cases to be similar with a preponderance of more severely injured cases, as may have confounded our study (Ryb and Dischinger, 2008; Brown et al., 2006b). Analysis of the odds of suffering an injury to a particular body region in overweight versus lean cases did show decreased odds for overweight cases suffering a significant extremity injury. This suggests that being overweight protects against extremity injuries. However, since the statistical significance was relatively weak (the upper limit of the 95% CI is 1.0) the clinical significance of this finding is unclear and a larger case series may need to be analyzed to confirm this association. A troubling finding in this study was that over half the cases were inappropriately restrained according to AAP recommendations. National Highway Traffic Safety Administration data from a 2000 report of rates of unrestrained children in motor vehicles ranged from as low as 5–10% in a cross-sectional survey to as high as 56% in motor vehicle collisions with a fatality (National Highway Traffic Safety Administration, 2007). Since we were applying the 2006 AAP guidelines for child restraints on a period of time starting 10 years prior, that number may be artificially elevated. In addition, this database was a convenience sample of patients. This may bias towards those who were not properly restrained being included in
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the database. This finding may also have confounded our results by selecting for more severely injured patients that would decrease the variability in injury severity and make it more difficult to differentiate any kind of relationship between severity and overweight status. Regarding the subject characteristics, our sample showed a distribution of overweight cases to be 35% of the cases. Other recent studies show similar distributions of overweight in pediatric patients (MMWR, 2006; Ogden et al., 2008). The incongruence in that 35% of cases fall in the top 15th percentile is a reflection of the increasing prevalence of overweight children in the population. A deliberate choice was made in creating the percentile charts to not include data from the most recent prevalence studies which reflect increased obesity to avoid misclassification of overweight children (Ogden et al., 2002). This further underscores the importance of evaluating overweight children and their possible risk for injuries or disease. A further limitation in looking at the subject characteristics is the significant preponderance of males in the overweight group. However, as some studies of overweight children show that more males than females are overweight, this difference is not unexpected (MMWR, 2006). Another group characteristic showing significant differences was age with the lean group being older than the overweight group. The small number of total cases may have been the limiting factor in demonstrating this difference. Nonetheless, the lack of difference in outcomes makes this disparity unimportant. Finally, the maximum intrusion was significantly greater in the lean group. Once again with no difference in the outcomes, this characteristic is likely irrelevant. In spite of this negative study focusing on overall injury severity, Brown’s study of pediatric patients admitted to intensive care units (ICU) after trauma describes worse outcomes for overweight pediatric patients after traumatic injuries with more complications and longer ICU stays in the obese patients, though less severe head injuries and no difference in overall severity of injury. However, the cohort was limited to severely injured patients only (Brown et al., 2006a). Adult studies also show worse outcomes for obese motor vehicle collision occupants. In a small study, Whitlock et al., found that adults with a higher BMI may be twice as likely to have a driver injury (Whitlock et al., 2003). Three further studies demonstrated that a higher BMI was associated with increased mortality in a motor vehicle collision (Arbabi et al., 2003; Zhu et al., 2006; Ryb and Dischinger, 2008). Finally, Mock et al., showed that each kilogram increase in weight increased risk of mortality in adults (Mock et al., 2002). Further larger studies and population-based studies may delineate a difference not appreciated here. Alternatively, looking at other markers of outcomes may show a disparity of clinical and statistical significance. Obesity will continue to be an epidemic to fight with its higher morbidity and mortality compared to the lean population. Disclaimer Data was provided by the Crash Injury Research and Engineering Network (CIREN) Project at the United States Department of Transportation/National Highway Traffic Safety Administration
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